drm/amd/display: dynamically clock gate before and after prefetch

drm/amd/display: dynamically clock gate before and after prefetch

[Why]
An invalidation request arriving during prefetch can potentially hang
the system if dynamic clock gating is enabled and memory power requests
are disabled.

[How]
• Disable clock gating and enable memory power requests for the duration
of the prefetch.
• Turn on clock gating and disable memory power requests again after
prefetch is complete.

Limit the scope for DCN35 and DCN42 only.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Leo Chen <leo.chen@amd.com>
Signed-off-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>